The invention relates to an apparatus for the manufacture of profiled plastic pipes.
In an apparatus of the generic type known from DE 31 20 480 A1 (corresponding to U.S. Pat. No. 4,492,551), actuation of the half shells, which combine in pairs to form a mold, takes place on the molding path by means of an upper driving pinion engaging with an indentation on the upper side of each half shell. Vacuum suction takes place via vacuum connections on the upper side of the machine bed which overlap vacuum channels at the beginning of the molding path; the vacuum channels are formed in the half shells. Equally, cooling water inlet lines and cooling water outlet lines discharge into the upper side of the machine bed, overlapping cooling water channels on the molding path which are formed in the half shells and discharge on the lower side of the half shells. It is essential that flat-spread and tight engagement exists between the sliding surface of the machine table, in particular in the area of the molding path, and the lower sides of the half shells, so that there is no vacuum loss in particular due to the fact that the air is sucked off between the lower side of the half shells and the sliding surface of the machine bed and not through the vacuum channels in the half shells. In this regard, the same applies to the cooling water, which must not escapexe2x80x94to a substantial extentxe2x80x94from between the lower side of the half shells and the slide surface of the machine table laterally of the molding path. When pipes of greater diameter ranges are to be made on apparatuses of the generic type, for instance pipes in a lower range of nominal diameters from 100 to 150 mm and in an upper range of nominal diameters of up to 400 mm, problems of leak-tightness between the under-sides of the half shells and the sliding surface of the machine bed arise in particular in the upper range of nominal width, leading to the specified drawbacks on the molding path.
Half shells for apparatuses for the manufacture of profiled plastic pipes are known from DE 197 00 028 A1, which are intended to be suitable also for extruders of great-diameter corrugated pipes. They have an indentation on their upper and lower side without any details being disclosed in this regard.
DE 43 18 514 C1 teaches an apparatus for the manufacture of profiled plastic pipes, in which two half shells are joined together on a molding path to form a mold; they are provided with indentations on their upper and lower side, each indentation engaging with a driving pinion. The known embodiment can only be used in so-called blow molding, in which air is blown at overpressure into the pipe that is to be produced. Problems of leak-tightness between the half shells and the machine bed do not occur.
We provide an apparatus of the generic type such that, even when half shells are used for the manufacture of pipes in the upper range of nominal width, there are no problems of leak-tightness between the lower sides of the half shells and the sliding surface of the machine bed, in particular in the area of the molding path.
The fact that it is possible to actuate the half shells that are designed for the manufacture of pipes of greater nominal diameter not only from above but also from below enables the half shells to be driven free from tilting on the molding path. This precludes any stress marks that might produce leaks to originate on the sliding surface of the machine bed. Only the half shells that serve for producing pipes of greater nominal diameters are actuated also from below, the half shells serving to produce pipes of smaller nominal diameters are only actuated from above.